@rcpinheiro I’ve tested this plugin with Cordova 7.1 and the builds were successful for both iOS and Android. If you have made any configuration related to this plugin in config.xml file, please remove it. That might be the reason why your build failed.

@mailpravink Did you test your app on standard (available at the store) Monaca Debugger? You need to test your app with custom Monaca Debugger because the api.ai plugin is not included in the standard Monaca Debugger. Please refer to:
How to build custom debugger for Android
How to build custom debugger for iOS